1. Field of the Invention
The present invention relates to an antenna for a vehicle, and more particularly, to an antenna for a vehicle that minimizes a return loss generated due to an effect of a vehicle loop ground.
2. Description of the Related Art
In general, a conventional communication for a vehicle receives a radio frequency signal such as an Amplitude Modulation (AM) and a Frequency Modulation (FM). For a signal reception of the existing AM and FM band, a glass antenna in which an antenna function is embedded to a window hot-wire has been widely used. In addition to this embedded glass antenna, an external antenna such as a whip antenna or a rod type pole antenna which connects a vertical conducting wire of a π/4 length to a coaxial cable and uses a vehicle itself as a ground connection is used.
Due to the development of communication technology, a vehicle is able to support a broadcasting such as a digital multimedia broadcasting (DMB), XM®, SIRIUS®, digital multimedia broadcasting (DMMB), digital television (DTV), code division multiple access (CDMA), and global positioning system (GPS), in addition to an AM/FM signal. Accordingly, the development of antenna suitable to broadcasting band is important, but the existing glass antenna may be insufficient to satisfy such a demand. In addition, due to an increase of an electronic sub assembly (ESA), the radiation noise of electronic equipment within a vehicle flows back into the vehicle via the vehicle antenna, affecting the reception performance of broadcasting. In particular, the glass antenna has a structure in which the radiation noise of electronic equipment of vehicle flows back into the vehicle, and the directivity of antenna is not identical in all directions (e.g., omnidirectional), thus decreasing the reception performance.
However, the shark fin shaped antenna mounted on a vehicle loop may implement a robust design (e.g., blocking by vehicle loop) in the directivity and the inflow of the radiation noise of electronic equipment unit of vehicle thus improving the reception performance of radio. However, reception sensitivity of antenna may occur due to the miniaturization of AM/FM radio. FIG. 1 is an exemplary detailed view illustrating a structure of a shark antenna for a vehicle which is used in the related art.
Referring to FIG. 1, the conventional shark antenna for the vehicle includes a case 11, a base 12, a printed circuit board 13, a chip antenna 14, and a helical antenna 15. The case 11 is shaped as a shark fin and has an open lower end, and accommodates the printed circuit board 13, the chip antenna 14, and the helical antenna 15. The chip antenna 14 receives a GPS or a CDMA signal, and the helical antenna 15 receives a DMB signal. The chip antenna 14 and the helical antenna 15 are electrically connected to the printed circuit board 13 respectively, and deliver the GPS or the CDMA signal, and the DMB signal received from each antenna to a coaxial cable which is connected to a receiver since a conductive pattern is formed in the printed circuit board 13.
The helical antenna 15 is an antenna made of a metal wire wound in the shape of a spiral helix. A height of the helical antenna is set to the height that may receive the DMB signal, however, it may not be possible to receive a low frequency signal such as an AM/FM with the helical antenna of the conventional shark antenna. The shark antenna is an antenna which has been designed in consideration of the vehicle aesthetics and a function of the antenna, however, the aesthetics of the vehicle may be deteriorated since the height of the shark antenna may be excessively increased when receiving a signal of a low frequency band such as an AM/FM with the helical antenna. In addition, due to a nature of a FM monopole shark antenna which is mounted to a vehicle loop, a return loss may be frequently generated due to the effect of the vehicle loop ground, and accordingly, an insufficient impendence matching of a radiation board may occur.